determining tg-43 brachytherapy dosimetry parameters and dose distribution for a 131cs source model cs-1

background: monte carlo determination of tg-43 brachytherapy dosimetry parameters and dose distribution calculation for 131cs source model cs-1 are presented in this study. materials and methods: the dose distribution was calculated around the 131cs model cs-1 located in the center of 30 cm ×30 cm ×30 cm water, and soft tissue phantoms cube using mcnp code by monte carlo method. the percentage depth dose (pdd) variation along the different axis, parallel and perpendicular, the source was calculated. then, the isodose curves for 100%, 75%, 50% and 25% pdd were constructed. finally, f(r,|θ|) and g(r) dosimetry parameters of tg-43 protocol have been determined. results: results obtained show that the monte carlo method could only calculate dose deposition in high gradient region, near the source, accurately. the energy cut off was found to be 1 ev and the error in the calculations was less than 2%. conclusion: the isodose curves of the cs-1 131cs source were constructed from dose calculation by mcnp code. the calculated dosimetry parameters for the source were in agreement with previously published results.